1. Field of the Invention
The present invention generally relates to medical devices and systems that incorporate an apparatus and method to assess the risk of R-on-T event, based on analysis of the surface ECG or the intracardiac electrogram (IEGM). The risk assessment of R-on-T event can be further used for risk stratification of ventricular tachyarrhythmias, prediction and prevention of ventricular tachycardiac (VT) and/or ventricular fibrillation (VF), and facilitating fast and robust detection of VT/VF onset.
The present invention particularly relates to implantable heart stimulators, including pacemakers, defibrillators and cardiovertors, which stimulate cardiac tissue electrically to control the patient's heart rhythm. The present invention also relates to external cardiac monitors, portable Holter monitors, and automatic external defibrillators (AEDs) that are capable to measure, record, and analyze the surface ECG.
2. Description of the Related Art
A R-on-T event is a premature ventricular event (R-wave) interrupting the T wave of the preceding beat. A R-on-T event often predisposes to serious ventricular arrhythmias.
With respect to artificial heart stimulators such as implantable cardiac pacemakers determination of the duration of an individual's R-T interval is important in order to prevent stimulation of the ventricle during this interval because the ventricular myocardium is not fully repolarized then. During the ventricular repolarization the ventricle is susceptible to fibrillation. Therefore, the time interval prior to the T-wave is called vulnerable period (VP). The T-wave precedes the end of the vulnerable phase.
The QT-RR relationship has been extensively investigated during the past decades. It is well known that the QT interval is rate-dependent. In order to compare the QT interval recorded at different heart rates, effort has been made to estimate the heart-rate corrected QT interval (QTc), which relates the QT interval with the RR interval in a predefined mathematical formula, based on statistical regression analysis. Although dozens of QTc formulas have been proposed (linear model, hyperbolic model, parabolic model, etc.), controversial results on optimal regression parameters have been reported.